Method and system for cooling the clutch system of a transmission

ABSTRACT

A method and apparatus for reducing the thermal load on a motor vehicle clutch system. The clutch includes at least a pressure plate, a clutch disk, and a flywheel, by way of which a torque is transmitted. The friction forces that exist on the respective friction surfaces of the clutch disk are unevenly distributed. The clutch is cooled by a flow of cooling air that is led through the clutch bell that encloses the clutch and that defines a housing. The cooling air is conducted from the existing ventilation air inlets of the vehicle, and a jet pump arranged in the exhaust system is disclosed for withdrawing the cooling air from the clutch housing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for the reduction of thermalloads and a method for cooling clutch systems, as well as a systemtherefor.

2. Description of the Related Art

It has been shown that the thermal economy in clutch systems, such as,for example, a dry friction clutch, is problematic, especially at highpower input. A thermal overload is especially to be suspected in aload-shift clutch of an uninterruptible transmission (USG).

The components of the clutch, especially the friction lining, have alimited temperature resistance, and the energy input is very high inrelation to the available space, whereby the heat transfer to theenvironment is too low.

In addition, the pressure plate, for example, has a smaller heatcapacity in contrast to the flywheel of the clutch. Furthermore, theheat flow to the surrounding parts is relatively low and the heattransfer to the surrounding air within the clutch bell housing is alsolow. Thus, there is a limit relative to the operation of the clutchsystem as a result of the expected temperature rise in known clutchsystems, especially of the pressure plate.

Therefore, especially in load-shift transmissions, it is a necessitythat the temperature load on the clutch be lowered by cooling measures.In the case of a so-called inline transmission, for example for a reardrive motor vehicle, an open type of construction, which of a certainsize makes cooling possible (tunnel assembly, water spray, near theexhaust system), can only be realized with limitations.

The object of the present invention is directed to a method and a systemof the above-described type that makes possible the optimal cooling of aclutch system of a power train, so that the operating conditions of theclutch system in particular are improved.

SUMMARY OF THE INVENTION

The object of the invention is particularly achieved by providing amethod for the reduction of the thermal load on a clutch system withwhich torque is transmitted. The clutch system includes at least apressure plate, a clutch disk, and a flywheel, whereby the frictionaltorque that exists at the time on the friction surfaces of the clutchdisk is unevenly distributed.

The frictional load generated in the clutch system is determined by thefrictional torque that acts and the relative speed. In known clutchsystems an identical speed condition at both friction surfaces of theclutch disk is preferred. A solution can consequently lie in producinguneven frictional torques on the respective friction surfaces. In thatway, the pressure plate, for example, can be supplied with a smallerportion of the frictional energy that occurs, so that the thermal loadis reduced.

Within the scope of the invention a further embodiment can be providedin which different friction linings with different coefficients offriction can be utilized at the two friction surfaces of the clutchdisk. The frictional load that is produced is thereby introducedunequally to the two friction surfaces by providing different frictionparameters at both frictional sides of the clutch disk.

The frictional torque that is generated depends on the effectivefriction radius, the contact pressure of the pressure plate, and thecoefficient of friction of the respective friction surfaces. Influencingthe clutch system coefficient of friction conditions provides thepossibility to suitably distribute the thermal load. It is alsoconceivable that the other influence values could be changed.

In the method in accordance with the invention several possibilities areprovided for influencing the coefficient of friction conditions in theclutch system, which are described below.

For example, a lower coefficient of friction can be utilized on thepressure-plate-side friction surface of the clutch disk than on theflywheel-side friction surface, so that a lesser amount of frictionalenergy is introduced on the pressure plate than on the flywheel. In thatway, a desired distribution of the frictional load can be realized.Thereby, in an advantageous way, lower thermal loads arise on thepressure plate.

In accordance with the invention, by the use of different frictionlinings on the clutch disk it can be provided that the respectivefriction partners on the flywheel-side are selected in such a way that ahigher coefficient of friction arises when the temperature increases.For example, the clutch disk can have different friction linings on itstwo friction surfaces. The friction partners on the flywheel-side havesuch a type of temperature dependence that a higher coefficient offriction arises with increasing temperature. If, as expected, a highertemperature arises at the friction point during the operation of theclutch, the coefficient of friction on the pressure plate sidedecreases, so that the desired coefficient of friction difference isadjusted.

In addition, in accordance with the invention it can be provided that inthe case of identical friction linings on the clutch disk two frictionpartners with different characteristics are utilized, so that thedesired coefficient of friction difference or frictional torquedistribution results. For example, the pressure plate and the flywheelcan be made from combinations of the materials steel and aluminum.

Furthermore, in the case of identical friction linings on the clutchdisk, it can be provided that the respective friction partners have sucha temperature dependence that a lower coefficient of friction ariseswith increasing temperature, whereby a higher temperature exists on thepressure plate than on the flywheel, so that the desired coefficient offriction difference is realized.

The previously-described possibilities can also be arbitrarily combinedin order to further improve the proposed method.

Alternatively, in the method in accordance with the invention it canalso be provided that a higher coefficient of friction is utilized onthe pressure-plate-side friction surface of the clutch disk, forexample, than on the flywheel-side friction surface if the pressureplate is suitably cooled. In that way, under certain circumstances,namely when cooling measures are carried out at the pressure plate, areverse friction load distribution is also conceivable. Thereby, ahigher temperature of the pressure plate, for example, can lead to analtogether better heat elimination at the clutch system by reason of ahigher temperature differential. At the same time, it must be noted,however, that a temperature-resistant friction lining must be utilizedat each friction surface as the friction lining.

Furthermore, the underlying object of the invention is also especiallyachieved in that a method is proposed for cooling the clutch in a powertrain of a motor vehicle, in which a flow of cooling air for the clutchis utilized. Furthermore, particularly for carrying out the method, asystem for cooling the clutch of a power train of a motor vehicle isproposed, wherein a flow of cooling air is provided that can beconducted through the clutch bell surrounding the clutch as a housing.

Advantages and additional embodiments of the system and the method inaccordance with the invention for cooling the clutch of a power trainare described in greater detail below.

In accordance with an advantageous further development of the invention,the already-existing air inlets of the motor vehicle, for example forthe ventilation of the interior, can be utilized as a cooling airflow tocool the clutch. Preferably, the flow of cooling air can be guidedthrough the clutch bell that surrounds the clutch as a housing.

For that purpose, the inlets, for example, could be designed anddimensioned accordingly. All together, the advantage of usingalready-existing air inlets is that, for example, filters, dirt pans,water drains, and the like, only have to be provided once in a motorvehicle because of their dual usage. In addition, by means of the airpassages provided, acoustic advantages can be realized in contrast withopen clutches.

Within the scope of an arrangement of the invention, the exiting coolair flow can be carried off to the environment using the existingexhaust gas system of the motor vehicle. The cool air flow can thus becarried off through the exhaust gas system together with the exhaustgas. Especially in motor vehicles with rear drive, the exhaust system islocated near the transmission. In accordance with that arrangement thereresults the advantage that in that way clutch noises are not consideredto be disturbing in the surrounding area because of the muffler.

Preferably, the cool air flow can be provided by a pump device providedin the exhaust gas flow of the exhaust gas system. The cool airflow canthereby be drawn off through the clutch bell. The pump device canespecially be a jet pump, or the like, which is preferably provided inthe exhaust gas stream. In that way, other necessary (active) coolingmeasures can be avoided.

It is also possible that the cool airflow is interrupted at leastperiodically through a shutter device in the exhaust system, so that anindependent stationary exhaust gas measurement is made possible.Preferably, at least a flap, or the like, can be utilized as a shutterdevice.

Preferably, the proposed system and method can be utilized in highperformance clutches, especially in a load-shift transmission (USG)and/or a double-clutch transmission (DKG).

BRIEF DESCRIPTION OF THE DRAWINGS

Additional advantages and embodiments follow from the dependent claimsand the following description and drawings in which:

FIG. 1 is a schematic view of a system for cooling a clutch with a jetpump; and

FIG. 2 is a graph with the results of a simulation calculation for amethod for reducing the thermal load of a clutch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

There is shown in FIG. 1 one possible embodiment of a system inaccordance with the invention to cool a clutch, whereby an engine 101with a connected exhaust gas system 102, and a transmission 103 with aclutch bell 104, as well as a drive shaft 105, are shown inschematically. In addition, there is shown in FIG. 1 an exemplaryexisting air inlet 107, for example for the windshield for ventilatingthe motor vehicle interior, which is utilized additionally for thecooling airflow in accordance with the invention. Other air inlets canalso be provided for the cooling airflow.

The cooling airflow can be withdrawn from the clutch bell 104 by meansof at least one air outlet 108 through a jet pump 106. The jet pump 106is located in the exhaust system 102, and which is shown larger in theFIG. 1 enlargement portion.

The system in accordance with the invention, by interconnection with theexisting air inlet system and exhaust gas system provided in the motorvehicle, can enable the supply and withdrawal of the cooling airflow inaccordance with the invention for the cooling of the clutch.

The system can especially be utilized in connection with a load-shifttransmission (USG), a double-clutch transmission (DKG), and all types ofhigh-performance clutches that require (air) cooling.

In FIG. 2 there is shown the result of a simulation calculation for amethod for reducing the thermal load on a clutch. There are showntherein different temperature trends over time.

The simulation model was prepared for a load-shift clutch of a USGsystem. In that way, the effect of the changed coefficients of frictioncan be shown.

Moreover, the coefficients of friction of the respective frictionsurfaces are assumed, one time with a constant ratio (1:1) and one timewith a ratio of 0.7:1. A plurality of maximum accelerations of the motorvehicle to a speed of 100 km/h were assumed as the loading. The uppercurve of the pressure plate temperature TDP signifies the coefficient offriction ratio of 1:1, while the lower curve shows the pressure platetemperature T_(DP) at the coefficient of friction ratio of 0.7:1.

One can clearly appreciate that the pressure plate temperature is lowerat a coefficient of friction ratio of 0.7:1. The temperatures of theflywheel T_(SR) by comparison increased only slightly. That isperceptible in the curve for T_(SR).

The patent claims included in the application are illustrative and arewithout prejudice to acquiring wider patent protection. The applicantsreserve the right to claim additional combinations of features disclosedin the specification and/or drawings.

The references contained in the dependent claims point to furtherdevelopments of the object of the main claim by means of the features ofthe particular claim; they are not to be construed as renunciation toindependent, objective protection for the combinations of features ofthe related dependent claims.

Although the subject matter of the dependent claims can constituteseparate and independent inventions in the light of the state of the arton the priority date, the applicants reserve the right to make them thesubject of independent claims or separate statements. They can,moreover, also embody independent inventions that can be produced fromthe independent developments of the subject matter of the includeddependent claims.

The exemplary embodiments are not to be considered to be limitations ofthe invention. On the contrary, many changes and variations are possiblewithin the scope of the invention in the existing disclosure, inparticular such variants, elements, and combinations and/or materialswhich, for example, are inventive by combining or modifying singlefeatures that are in combination and are described individually inrelation to the general specification and embodiments as well as theclaims and shown in the drawings, as well as elements or method stepsthat can be derived by a person skilled in the art in the light of thedisclosed solutions of the problem, and which by means of combinedfeatures lead to a new object or new method steps or sequences of methodsteps, as well as manufacturing, testing, and operational procedures.

1. A method for reducing the thermal load in a clutch system thatincludes at least a pressure plate, a clutch disk, and a flywheel, saidmethod comprising the steps of: transmitting a torque between respectivefriction surfaces of the pressure plate, the clutch disk, and theflywheel, and unevenly distributing frictional torque that acts at eachfriction surface of the clutch disk.
 2. A method in accordance withclaim 1, including the step of providing different friction linings withdifferent coefficients of friction on respective opposite frictionsurfaces of the clutch disk.
 3. A method in accordance with claim 1,including the step of providing a lower coefficient of friction on apressure-plate-side friction surface of the clutch disk than on aflywheel-side friction surface of the clutch disk, so that a smalleramount of frictional energy is introduced into the pressure plate thaninto the flywheel.
 4. A method in accordance with claim 3, including thestep of providing on the flywheel-side of the clutch disk a frictionlining having a higher coefficient of friction at increasingtemperature.
 5. A method in accordance with claim 1, including the stepof providing identical friction linings on respective sides of theclutch disk, and providing different friction characteristics at apressure-plate to clutch disk interface and at a flywheel to clutch diskinterface for a desired frictional torque distribution.
 6. A method inaccordance with claim 5, wherein the friction characteristics of atleast one of the pressure plate and the flywheel are provided by acombination of steel and aluminum friction surfaces.
 7. A method inaccordance with claim 1, wherein the clutch disk has identical frictionlinings on respective sides thereof and each friction exhibits suchinterface has a temperature dependence in the case of identical toprovide a lower coefficient of friction with increasing temperature,whereby a higher temperature occurs at the pressure plate than at theflywheel, so that a desired coefficient of friction difference isrealized at the pressure plate and the flywheel sides of the clutchdisk.
 8. A method in accordance with claim 1, wherein a highercoefficient of friction exists at a friction surface on thepressure-plate side of the clutch disk than at a friction surface on theflywheel side when the pressure plate is cooled.
 9. A method inaccordance with claim 8, wherein a temperature-resistant friction liningis utilized as the friction lining at each friction surface.
 10. Amethod in accordance with claim 1, including the step of introducing acooling airflow into a housing that surrounds the clutch.
 11. A methodin accordance with claim 10, including the step of utilizing at leastone existing air inlet for the ventilation of the interior of a motorvehicle as an inlet for the cooling airflow, and conducting the coolingairflow through the clutch housing.
 12. A method in accordance withclaim 10, wherein cooling airflow is withdrawn from the housing to theenvironment through an existing exhaust system of the vehicle.
 13. Amethod in accordance with e claim 10, wherein the cooling airflow isprovided by a pump means positioned in the exhaust gas flow of theexhaust system.
 14. A method in accordance with claim 13, wherein thepump means is a jet pump.
 15. A method in accordance with claim 10,including the step of Periodically interrupting the cooling airflow by ablocking means to allow a stationary exhaust gas measurement
 16. Amethod in accordance with claim 15, wherein the blocking means is ashutter.
 17. A method in accordance with claim 10, wherein the clutch isincluded in a power train that includes one of a load-shift transmissionand a double-clutch transmission.
 18. A system for cooling a clutch in amotor vehicle power train, said system comprising: a flywheel, a clutchdisk, and a pressure plate, wherein the flywheel and the pressure platefrictionally engage respective opposed surfaces of the clutch disk, aclutch bell that surrounds at least the clutch disk and the pressureplate as a clutch housing, and means for introducing a cooling airflowinto the clutch housing.
 19. A system in accordance with claim 18,wherein the means for introducing cooling airflow includes as an airinlet at least one existing air inlet for the ventilation of theinterior of the motor vehicle.
 20. A system in accordance with claim 18,wherein an existing exhaust system of the motor vehicle is incommunication with the clutch housing for withdrawal of cooling airflowfrom the clutch housing.
 21. A system in accordance with one claim 20,including pump device is means in the exhaust gas flow of the exhaustsystem for producing the cooling airflow.
 22. A system in accordancewith claim 21, wherein the pump means includes at least one jet pump.23. A system in accordance with claim 20, including blocking is meansprovided in the exhaust system for blocking flow into an exhaust gasstream of cooling airflow from the clutch housing.
 24. A system inaccordance with claim 23, wherein the blocking means is a shutter.
 25. Asystem in accordance with claim 18, wherein the system is incorporatedinto a motor vehicle power train that includes a high-performanceclutches clutch and at least one of a load-shift transmission and adouble-clutch transmission.